I think my best Ebay deal was selling my old Thinkpad 600 for a bit less than $300, that was. . 5 years ago, maybe. Other than that a smattering of communication parts and LCD panels here and there. . .
The worst was a CAAD8 for $620 ($540 + $80) from some guy in Florida that decided he couldn't ship it for $80 (I guess he didn't get much as he wanted), so I had to open a paypal claim for my money back.